In document handling devices of the type described for example in U.S. Pat. No. 4,054,092 issued Oct. 18, 1977 and assigned to the assignee of the present invention, there is taught therein apparatus for bottom feeding of documents placed in an infeed hopper, and passage through a region containing feed means and stripper means to separate documents so as to be passed from the aforesaid region toward an outfeed stacker on a one at a time basis, the stripping action serving to assure the delivery of single fed documents under normal conditions.
As the documents leave the aforesaid region, they come under the influence of acceleration means which abruptly accelerates the document which has just left the influence of the drive and stripper means so as to form a gap of at least a predetermined length between the document being accelerated and the next succeeding document to be accelerated. This gap is utilized, in conjunction with light means such as an LED and light sensing means such as a phototransistor to detect the change in brightness in order to distinguish the movement of a document between the light source and light sensing element from the passing of a gap therebetween.
The documents continue to move from this location where they are neatly stacked in an outfeed stacker.
In many operations it is quite often necessary to be absolutely assured that the document count be exact. For example, when counting currency and especially when counting currency of large denominations, an error in the count of documents, no matter how small, is nevertheless cause for great concern.
One of the problems which contributes to the possibility that such errors might occur is the possibility that the currency, when in use, may acquire or have deposited thereon sticky or adhesive material or may have creases or other mutiliations which cause two documents to adhere to one another and to fail to separate even as a result of the stripping operation. If two such documents are fed so that one is directly super-imposed upon the other, the apparatus will count this anomaly as a single document, thus throwing off the count. It is therefore imperative in many applications to provide means for positively and reliably detecting such conditions.
In addition to the above, and due to the fact that the documents being counted may be vastly different in age and amount of use, as well as the fact that they may be fed in any one of four different orientations, the problem of distinguishing between single fed documents and double fed documents is compounded.